The London Stock Exchange Group (LSEG) has drafted in a City heavyweight to conduct an independent probe of the boardroom crisis which triggered the ousting of its former chief ex‎ecutive.

Sky News has learnt that Donald Brydon, the company's chairman, has written to its 20 largest shareholders to inform them of the review.

It is being led by Simon Collins, the former UK chairman of KPMG - the "big four" audit firm.

An investor who has been briefed on the probe said that Mr Collins had been given access to relevant LSE documents as well as board members including Xavier Rolet, whose departure late last year sent shockwaves through the City.

The independent review has been underway for several weeks, according to the investor, and is expected to lead to a report being presented by Mr Collins to the LSE in a few weeks' time.

The board's decision to commission the independent investigation followed one of the most extraordinary shareholder battles at a blue-chip British company for years.

Sir Christopher, who has a close relationship with Mr Rolet, was infuriated at the company's decision to announce the Frenchman's retirement last autumn, and waged a bitter campaign to oust Mr Brydon.

The TCI boss also sought to have Mr Rolet reinstated, but abandoned that ‎effort when he said he would not return to the LSE under any circumstances.

The row, which drew in the governor of the Bank of England and chief executive of the Financial Conduct Authority, culminated in defeat for Sir Christopher at an extraordinary general meeting in December.

However, many investors expect him to restart the battle if he is dissatisfied with the choice of Mr Rolet's successor.

The LSE's parent, which reported full-year results on Friday, said it was making good progress in the search‎ for a new chief executive, and that it was considering a high-quality field of candidates.

The selection of a new boss will be among the final big assignments facing Mr Brydon, who has said he will step down next year.

The row sparked by Mr Rolet's "retirement" stunned the City because he had planned to leave in any case if a merger between the LSE and Germany's Deutsche Boerse - which was ultimately blocked by regulators last year - had been completed.

Shareholders now say they have been told that the LSEG has ruled out appointing an internal successor to Mr Rolet - which if true would mean that Mark Makepeace, its group director of information services and the boss of its FTSE Russell indices business, ‎is not on the shortlist.

It would also rule out Raffaele Jerusalmi, chief executive of the LSE-owned Borsa Italiana.

David Warren, the LSEG's chief financial officer, took over as interim chief executive following Mr Rolet's sudden exit, but has no interest in taking the role permanently.

Sources say the company could announce the name of its new chief executive this month.

The news of Mr Collins' inquiry comes weeks after Sir Christopher told his investors last week that the LSE was likely to be targeted by an American rival as part of a wave of consolidation of the exchanges sector.

The LSE Group has a market value of just over £13bn, meaning that with a typical takeover premium attached, any deal involving the entire company could value it at £15bn or more.

His comments were significant because Sir Christopher has close ties to Jeff Sprecher, IntercontinentalExchange Group's (ICE) chairman and chief executive.

ICE has frequently been tipped as a likely suitor for the London bourse's parent company.

The LSEG declined to comment this weekend on Mr Collins' review, while Mr Collins could not be reached.